Spinal implant having deployable bone engaging projections

ABSTRACT

Instrumentation is disclosed for inserting an interbody spinal fusion implant for implantation at least in part within and across the generally restored height of a disc space between two adjacent vertebral bodies of a human spine. The implant has an external housing and a substantially hollow internal rotatable member having bone engaging projections that are deployable through the housing to penetrably engage the adjacent vertebral bodies.

This application is a continuation of application Ser. No. 13/050,761,filed Mar. 17, 2011, now U.S. Pat. No. 8,579,982; which is a divisionalof application Ser. No. 12/806,314, filed Aug. 10, 2010, now U.S. Pat.No. 7,972,365; which is a continuation of application Ser. No.11/527,377, filed Sep. 25, 2006, now U.S. Pat. No. 7,771,475; which is adivisional of application Ser. No. 10/746,183, filed Dec. 24, 2003, nowU.S. Pat. No. 7,112,206; which is a divisional of application Ser. No.10/062,805, filed Feb. 2, 2002, now U.S. Pat. No. 6,923,830; all ofwhich are incorporated herein by reference.

BACKGROUND

Push-in spinal fusion implants (allowing for the growth of bone fromadjacent vertebral body to adjacent vertebral body through the implant)having upper and lower surfaces adapted for placement by linearinsertion within a disc space and in contact with the adjacent vertebralbodies are known in the related art. Such a push-in spinal fusionimplant was invented by Michelson and is disclosed in U.S. Pat. No.5,776,199, filed Jun. 28, 1988, which is hereby incorporated byreference. Push-in spinal fusion implants offer the advantage of beingeasily positioned in the implantation space and of having the ability tohave varying height to width ratios.

Lordotic or tapered, push-in spinal fusion implants are also known inthe art. By way of example, Michelson has invented such implants asdisclosed in U.S. Pat. No. 5,609,635, filed Jun. 7, 1995, which ishereby incorporated by reference. Lordotic or tapered, spinal fusionimplants may more easily restore or enhance spinal lordosis.

Spinal fusion implants having projections that can be deployed after theimplant has been inserted into the disc space are also known in therelated art. An example of a spinal fusion implant having deployableprojections was invented by Michelson and also is disclosed in U.S. Pat.No. 5,776,199 previously incorporated by reference herein. Otherexamples of implants having deployable projections include, but are notlimited to, U.S. Pat. No. 6,179,873 to Zientek and InternationalPublication No. WO 01/01894 A1 to Bolger et al. Examples of spinalfusion implants having rotatable elements for fixing the implant to thevertebrae include U.S. Pat. No. 6,210,442 to Wing et al., U.S. Pat. No.6,090,143 to Meriwether et al., and U.S. Pat. No. 5,888,228 to Knothe etal.

None of the related art implants have a rotatable internal member withbone engaging projections that are retracted within the interior of theimplant to permit the implant to be inserted into the disc space andthen deployed to extend through the exterior of the implant topenetrably engage the adjacent vertebral bodies, while permitting bonegrowth from adjacent vertebral body to adjacent vertebral body throughthe interior of the implant and the interior of the internal rotatablemember substantially unimpeded by the internal rotatable member and boneengaging projections.

There exists a need for a spinal fusion implant providing for all of theaforementioned features in combination.

SUMMARY OF THE INVENTION

In accordance with the present invention, as embodied and broadlydescribed herein, there is provided a spinal fusion implant forimplantation at least in part within and across the generally restoredheight of a disc space between two adjacent vertebral bodies of a humanspine having an external housing with a substantially hollow internalrotatable member having bone engaging projections that are in aretracted position within the interior of the housing to permit theassembled implant to be inserted into the disc space. The internalrotatable member may be inserted into the housing prior to insertion ofthe implant into the disc space, or alternatively, the housing may beinserted into the disc space and the internal rotatable member can besubsequently inserted into the housing. The implant is preferablyinserted into the disc space by linear insertion without substantialrotation of the implant. Alternatively, the implant be can be rotated atleast in part generally less than 180 degrees during its implantationinto the disc space and is not screwed into the disc space. Afterinsertion, the internal rotatable member is rotated to a deployedposition so that the bone engaging projections extend through theexterior of the housing to penetrably engage the adjacent vertebralbodies to resist expulsion of the implant from the disc space, to gainaccess to the more vascular bone of the vertebral bodies further fromthe bone surfaces adjacent the disc space, to stabilize the adjacentvertebral bodies relative to the implant, and to stabilize the vertebralbodies relative to each other. The spinal implant is configured topermit bone growth from adjacent vertebral body to adjacent vertebralbody through the housing and through the interior of the internalrotatable member preferably substantially unimpeded by further internalmechanisms.

In one embodiment, the spinal implant of the present invention has anexternal housing having a hollow interior and a substantially hollowrotatable member therein. The implant and each of the hollow components,that is the housing and the internal rotatable member, are adapted tohold fusion promoting substances, such as but not limited to bone. Thehousing preferably has relatively thin walls, openings, and except forthe openings preferably a relatively smooth exterior. The rotatablemember has an open interior configured to hold bone growth promotingmaterial and at least one aperture therethrough in communication withthe open interior to permit for the growth of bone therethrough. Therotatable member preferably, but not necessarily, has a generallycylindrical or frusto-conical configuration, is preferably thin-walled,and is preferably in contact with the external housing, but is free torotate therein sufficient for its intended purpose. The rotatable memberhas bone engaging projections adapted to penetrably engage the bone ofthe adjacent vertebral bodies by rotating the rotatable member. Therotatable member is adapted to rotate within the hollow interior of theimplant between a retracted position and a deployed position. The boneengaging projections extend through at least some of the openings in theupper and lower surfaces of the implant so as to penetrate the vertebralbodies adjacent the disc space to be fused deep to the adjacentsuperficial endplate surfaces when deployed.

In a preferred embodiment, the bone engaging projections have ablade-like configuration oriented transverse to the longitudinal axis ofthe rotatable member with a leading edge and a trailing edge angledrelative to each other to form an apex adapted to penetrate the bone ofa vertebral body. The bone engaging projections are preferably orientedon opposite sides of the rotational member and may, but need not, bediametrically opposite one another. The bone engaging projections may bearranged such that at least the apexes of two opposite bone engagingprojections are on opposite sides of a mid-line passing therethrough.Such an over-center arrangement of the bone engaging projections createsa more stable configuration of the implant when the bone engagingprojections are fully deployed. Greater energy is required to de-rotatethe rotatable member with opposed bone engaging projections in anover-center arrangement as the apex of each bone engaging projection hasto be moved through the mid-line to move from a deployed to a retractedposition.

The spinal implants of the present invention may have upper and lowersurfaces that are generally parallel or angled relative to one another.The spinal implants of the present invention may have a cross-sectiontransverse to the longitudinal axis of the implant that is generallysquare, rectangular, or any other configuration suitable for itsintended purpose. The spinal implants of the present invention may havethe width equal to the height, the width greater than the height, or thewidth less than the height. The spinal implants of the present inventionmay have more than one rotatable member with bone engaging projections.The rotatable member can have a generally cylindrical configuration, agenerally frusto-conical configuration, or any other configurationsuitable for the intended purpose.

The present invention is also directed to an implant inserter instrumentadapted to insert the spinal implant into an implantation site anddeploy the bone engaging projections. The inserter instrument isconfigured to cooperatively engage the trailing end of the implant torotate the rotatable member to deploy the bone engaging projections. Thepresent invention is also directed to the methods for inserting anddeploying a spinal implant in accordance with the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a rear perspective view of a lumbar segment of a spine withthe dural sac retracted to the left showing a prepared recipientimplantation site with a guard for providing guided access to the discspace and an embodiment of an inserter instrument and an embodiment ofan implant in accordance with the present invention attached theretoapproaching the disc space between the adjacent vertebral bodies.

FIG. 2 is a fragmented side elevation view of the inserter instrumentand implant of FIG. 1.

FIG. 3 is a cross sectional view of the implant of FIG. 1 taken alongline 3-3 of FIG. 2.

FIG. 4 is an exploded perspective view of the trailing end of theimplant of FIG. 1 and the rotatable member having deployable boneengaging projections.

FIG. 5 is a partial perspective view of the leading end of the implantand the inserter instrument of FIG. 1 shown with bone engagingprojections in a deployed position.

FIG. 6 is an exploded perspective view of the leading end of implant ofFIG. 1.

FIG. 7 is a cross sectional end view of another embodiment of an implantwith the bone engaging projections in a retracted position in accordancewith the present invention.

FIG. 8 is a cross sectional side view of the implant of FIG. 7 takenalong line 8-8 of FIG. 7.

FIG. 9 is a cross sectional end view of the implant of FIG. 7 with thebone engaging projections in a deployed position.

FIG. 10 is a cross sectional top view of another embodiment of animplant in accordance with the present invention.

FIG. 11 is a cross sectional trailing end view of the implant of FIG. 10with the bone engaging projections in a retracted position.

FIG. 12 is a cross sectional end view of the implant of FIG. 10 withbone engaging projections in a deployed position.

FIG. 13 is a front perspective view of another embodiment of an implantin accordance with the present invention with the bone engagingprojections in a retracted position.

FIG. 14A is a cross sectional view along line 14-14 of FIG. 13.

FIG. 14B is a cross sectional view similar to FIG. 14A of an alternativeembodiment of an implant in accordance with the present invention.

FIG. 15 is a cross sectional view along line 14-4 of FIG. 13 with thebone engaging projections in a deployed position.

FIG. 16 is a front perspective view of another embodiment of an implantin accordance with the present invention with the bone engagingprojections in a retracted position.

FIG. 17 is a cross sectional view along line 17-17 of FIG. 16.

FIG. 18 is a cross sectional view along line 17-17 of FIG. 16 with thebone engaging projections in a deployed position.

FIG. 19 is a fragmented cross sectional view along line 19-19 of FIG.18.

FIG. 20 is an enlarged fragmentary view of a rotatable member and a boneengaging projection of another preferred embodiment of an implant inaccordance with the present invention.

FIG. 21 is an enlarged fragmentary view of a rotatable member and a boneengaging projection of yet another preferred embodiment of an implant inaccordance with the present invention.

FIG. 22 is a front perspective view of another preferred embodiment ofan implant in accordance with the present invention with the boneengaging projections in a retracted position.

FIG. 23 is an exploded side elevation view of the implant of FIG. 22.

FIG. 24 is a top plan view in partial cross section of another preferredembodiment of an implant in accordance with the present invention withthe bone engaging projections in a retracted position.

FIG. 25 a partial cross sectional end view along line 24-24 of FIG. 25with the bone engaging projections in a retracted position shown insolid line and in a deployed position shown in hidden line.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference will now be made in detail to the present preferredembodiments (exemplary embodiments) of the invention, examples of whichare illustrated in the accompanying drawings. Wherever possible, thesame reference numbers will be used throughout the drawings to refer tothe same or like parts.

FIGS. 1-6 show a preferred embodiment of a spinal implant 100 and apreferred embodiment of an implant inserter 200 in accordance with thepresent invention. Implant 100 has an external housing 101 with aleading end 102 for insertion first into the disc space between twoadjacent vertebral bodies of the human spine, a trailing end 104opposite leading end 102, an upper surface 106, a lower surface 108, andsides 110, 112 between upper and lower surfaces 106, 108. Leading end102 may be tapered to facilitate insertion of implant 100 into the discspace. Housing 101 of implant 100 preferably has at least a portionalong its longitudinal axis L that has a generally square cross sectiontransverse to the longitudinal axis L. It is appreciated that housing101 can have a generally rectangular cross section or othercross-sectional configuration suitable for its intended purpose. Housing101 preferably has a hollow interior 114 configured to hold bone growthpromoting material. In this embodiment, upper and lower surfaces 106,108 are preferably at least in part non-arcuate. Upper and lowersurfaces 106, 108, of housing 101 preferably each have at least oneopening 116 in communication with hollow interior 114 and adapted topermit the growth of bone from adjacent vertebral body to adjacentvertebral body through housing 101. Upper and lower surfaces 106, 108further preferably have a plurality of openings 118 configured to permitthe passage therethrough of bone engaging projections 132 describedbelow from hollow interior 114 to the exterior of housing 101. Sides110, 112 of implant 100 can also have openings 116.

Implant 100 has an internal rotatable member 120 configured to bepreferably at least in part within hollow interior 114 of housing 101and as shown in this embodiment is insertable within hollow interior 114by the user. While in this embodiment, rotatable member 120 is shownentirely within hollow interior 114 of housing 101, it is appreciatedthat the rotatable member need not be entirely within hollow interior114. For example, the rotatable member may have an external flange thatis at least in part outside of hollow interior 114. Rotatable member 120is preferably substantially hollow and has a leading end 122, a trailingend 124, an exterior surface 126, and an open interior 128. Trailing end124 preferably is configured to cooperatively engage an instrument forrotating rotatable member 120 such as, for example, inserter 200(described below). For example, the inner perimeter of trailing end 124can be hex-shaped or have any other configuration suitable forcooperatively engaging an instrument for rotating rotatable member 120.Exterior surface 126 of rotatable member 120 preferably has at least oneopening 130 that permits bone to grow therethrough. Preferably, at leastone of openings 130 in rotatable member 120 is configured to generallyalign with at least one of openings 116 in housing 101 to allow bone togrow from adjacent vertebral body to adjacent vertebral body thoughhousing 101 and through rotatable member 120.

The upper and lower surfaces of rotatable member 120 have at least onebone engaging projection 132 adapted to penetrably engage the bone ofthe adjacent vertebral bodies. Bone engaging projections 132 arepreferably configured such that when rotatable member 120 is in aretracted position, implant 100 may be linearly inserted into the discspace. After implant 100 is inserted into the disc space, rotatablemember 120 is moved to a deployed position so that bone engagingprojections 132 penetrably engage the endplates of an adjacent vertebralbody and prevent expulsion of implant 100 from the disc space.

In a preferred embodiment, bone engaging projections 132 have ablade-like configuration oriented transverse to the longitudinal axis ofrotatable member 120 with a leading edge and a trailing edge angledrelative to each other to form an apex adapted to penetrate the bone ofa vertebral body. The blade-like bone engaging projections 132 arepreferably of appropriate thickness, shape and sharpness to penetratethe vertebral bodies adjacent the disc space to be fused deep to theadjacent superficial endplate surfaces when the implant is in thedeployed position. Bone engaging projections 132 are preferably orientedon opposite sides of rotational member 120 and may, but need not, bediametrically opposite one another. Bone engaging projections 132 may bearranged such that at least the apexes of two opposite bone engagingprojections 132 are on opposite sides of a mid-line passingtherethrough. Such an over-center arrangement of bone engagingprojections 132 creates a more stable configuration of the implant whenthe bone engaging projections are fully deployed. Greater energy isrequired to de-rotate a rotatable member with opposed bone engagingprojections when in an over-center arrangement as the apex of each boneengaging projection has to be moved through the mid-line to move from adeployed to a retracted position.

As will be appreciated by those skilled in the art, bone engagingprojections other than blades may be employed that are suitable for theintended purpose. The number and orientation of the bone engagingprojections along rotatable member 120 may be varied without departingfrom the broad scope of the present invention. For example, at least twoof the bone engaging projections may be arranged at an angle to theouter surface of rotatable member 120, the angle may be 90 degrees or anangle other than 90 degrees to enhance the resistance of implant 100 toexpulsion from the disc space. As another example, bone engagingprojections 132 may also be oriented parallel to one another along atleast a portion of the longitudinal axis of implant 100.

As shown in FIG. 3, interior surface 134 of hollow interior 114 ofhousing 101 preferably forms a pair of opposed abutment surfaces 136.Abutment surfaces 136 are configured to support and permit rotatablemember 120 to rotate within hollow interior 114 from a retracted to adeployed position to deploy bone engaging projections 132. The rotationof rotatable member 120 is limited when bone engaging projections 132contact abutment surfaces 136. The rotation of rotatable member 120 canbe limited to approximately 180 degrees or less about its axis ofrotation so that it takes a half turn or less of the rotatable member todeploy the bone engaging projections. By way of example only and notlimitation, the rotation of rotatable member 120 can be limited to arange of approximately 25 degrees to approximately 65 degrees to movebone engaging projections from a retracted to a deployed position.Abutment surfaces 136 also may be configured to limit the rotation ofrotatable member 120 to approximately 90 degrees or less about its axisof rotation so that it takes a quarter turn or less of the rotatablemember to deploy the bone engaging projections. Interior surface 134 ofhollow interior 114 preferably has spaces 135 within the hollow interior114 of housing 101 configured to receive bone engaging projections 132in the retracted position such that the apex of each bone engagingprojection is substantially in a corner of hollow interior 114. In thisposition, the bone engaging projections are retained substantiallywithin the hollow interior of housing 101.

Abutment surfaces 136 also preferably form a shoulder 138 within hollowinterior 114 proximate trailing end 104 of housing 101 that isconfigured to permit and support the insertion of rotatable member 120into hollow interior 114 and retain rotatable member 120 therein in thedeployed position. Shoulder 138 also is preferably configured to contactimplant an engagement surface 212 of inserter 200 as will be describedbelow. The interior surface of hollow interior 114 also preferably has apair of opposed grooves 140 proximate trailing end 104 that are adaptedto engage tabs 214 of inserter 200. It is appreciated that trailing end104 may have any configuration known to those skilled in the artsuitable for cooperatively engaging an appropriate insertion instrument.

As shown in FIGS. 5 and 6, rotatable member 120 is insertable intohollow interior 114 of housing 101. After rotatable member 120 isinserted into hollow interior 114 and implant 100 is inserted into thedisc space, rotatable member 120 is rotated such that bone engagingprojections 132 extend through openings 118 to project above upper andlower surfaces 106, 108 of housing 101. It is appreciated that upper andlower surfaces 106, 108 can have any openings suitable for the intendedpurpose of deploying bone engaging projections or other means forachieving the same purpose. Further, openings 118 can be in the form ofslots wherein the slots are configured to be in close tolerance withbone engaging projections 132 so as to support bone engaging projections132 when deployed.

As shown in FIG. 4, hollow interior 114 of housing 101 and open interior128 of rotatable member 120 are configured to hold bone growth materialstherein. Examples of such bone growth materials include, but are notlimited to, any of, or any combination of, bone in any of its forms,materials derived from bone, bone morphogenetic proteins, mineralizingproteins, genetic materials coding for the production of bone or anysubstance capable of inducing the formation of bone or useful forachieving fusion for the intended purpose. The rotation of rotatablemember 120, when rotated between a retracted and a deployed position,does not substantially displace bone growth material from within hollowinterior 114 of housing 101 and/or open interior 128 of rotatable member120. Accordingly, implant 100 and rotatable member 120 can be loadedwith bone growth material prior to insertion of the implant into thedisc space and prior to deployment of the bone engagement projections.Alternatively, housing 101 and rotatable member 120 can be loaded withbone growth material after insertion of the implant at least in partwithin the disc space either before or after rotation of rotatablemember 120 and may be further loaded after deployment of the boneengaging projections as desired.

FIGS. 1, 2 and 5 show a preferred implant inserter 200 for use with theimplant of the present invention. Inserter 200 preferably has an outershaft 202 with a distal end 204, a proximal end 206, and a reduceddiameter medial portion 208. Distal end 204 preferably has a headportion 210 with an implant engagement surface 212 located distallythereto. Head portion 210 preferably has a cross section transverse tothe longitudinal axis of inserter 200 corresponding to the transversecross sectional configuration of at least the outer perimeter oftrailing end 104 of implant 100.

Implant engagement surface 212 is preferably sized and shaped tocooperatively contact shoulder 138 of hollow interior 114 of housing101. Implant engagement surface 212 also preferably has opposed tabs 214that are adapted to snap into grooves 140 of housing 101.

Head portion 210 also preferably has a pair of longitudinal recesses 216extending between an upper surface 218 and a lower surface 220 of headportion 210. Recesses 216 permit head portion 210 to be resilientlycompressed so that tabs 214 may be inserted into grooves 140 of housingand then locked into place when released. Outer shaft 202 alsopreferably has a handle 222 at its proximal end 206.

Inserter 200 also has an inner shaft 224 that is rotatable within outershaft 202. Inner shaft 224 has a distal end 226 and a proximal end 228.Distal end 226 of inner shaft 224 has rotational engagement surface 230that is preferably configured to cooperatively engage trailing end 124of rotatable member 120. In a preferred embodiment, rotationalengagement surface 230 is hex-shaped. Proximal end 228 of inserter 200preferably has a handle 232 with an outer perimeter corresponding to theouter perimeter of handle 222 of outer shaft 202. Handle 232 ispreferably proximal of handle 222 so that the surgeon may rotate innershaft 224 via handle 232 while holding handle 222. In a preferredembodiment, inserter 200 preferably stabilizes housing 101 of implant100 while rotating rotatable member 120 to deploy bone engagingprojections 132. Inserter 200 is preferably a combination holder,driver, extractor, housing stabilizer, and rotator all in one.

While a preferred embodiment of an inserter 200 is shown, it isappreciated that any other inserter suitable for the intended purposeknown to those skilled in the art may be used to insert the implants ofthe present invention.

In FIGS. 7-9, another preferred embodiment of the implant of the presentinvention is shown and generally referred to by the reference number300. Implant 300 is similar to implant 100 but has a height that isgreater than its width. Implant 300 preferably has a housing 301 withupper and lower surfaces 306, 308 that are angled with respect to oneanother so as to maintain the natural lordosis of the spine afterimplantation. For example, upper and lower surfaces 306, 308 may be in adiverging or converging angular relationship to each other along atleast a portion of the longitudinal axis of implant 300. Similarly,sides 310, 312 can be angled relative to one another. It is appreciatedthat implant upper and lower surfaces 306, 308 and sides 310, 312 neednot be angled.

Implant 300 has a rotatable member 320 that is preferably frustoconicalin shape. Rotatable member 320 has bone engaging projections 332 adaptedto penetrably engage the bone of the adjacent vertebral bodies. Boneengaging projections 332 are preferably configured such that in aretracted position, implant 300 may be linearly inserted into the discspace. After implant 300 is inserted into the disc space, bone engagingprojections 332 are moved to a deployed position to penetrably engagethe endplates of each adjacent vertebral body and prevent the expulsionof implant 300 from the disc space. The rotation of rotatable member 320can be limited to approximately 180 degrees or less about its axis ofrotation so that it takes a half turn or less of the rotatable member todeploy the bone engaging projections. By way of example only and notlimitation, the rotation of rotatable member 320 can be limited to arange of approximately 25 degrees to approximately 65 degrees to movebone engaging projections from a retracted to a deployed position.

To support and facilitate the rotation of rotatable member 320, hollow314 of housing 301 preferably has a second shoulder 342 proximate to afirst shoulder 338. First shoulder 338 is preferably configured forengagement with the distal end of a suitably configured inserter 200.Second shoulder 342 supports a trailing end 324 of rotatable member 320.A leading end 322 of rotatable member 320 preferably has a cylindricalextension 344 for insertion into an opening 346 at leading end 302 ofhousing 301. Cylindrical extension 344 serves as an axle to supportleading end 322 and permit rotation of rotatable member 320 withinhollow 314 of implant 300. Rotatable member 320 may have openings in itssurface along its longitudinal axis to permit bone to grow throughrotatable member 320 and have an open interior.

In FIGS. 10-12, another preferred embodiment of the implant of thepresent invention for insertion into the spine from an anterior approachis shown and generally referred to by the reference number 400. Implant400 is similar to implant 300 except that it has a width greater thanits height and has two rotatable members 420 within hollow interior 414of housing 401. Housing 101 preferably has upper and lower surfaces 406,408 that are angled with respect to one another and an overall widththat is generally greater than one half the width of the disc space intowhich implant 400 is to be inserted.

Trailing end 404 of housing 401 may have an anatomical configuration toutilize the apophyseal rim bone around the perimeter of each vertebralbody to help support the implant, and/or avoid the need to deeplycountersink the implant so as to avoid a lateral corner of the implantfrom protruding beyond the perimeter of the vertebral bodies. Examplesof such configurations are in U.S. Pat. No. 6,241,770 to Michelson,entitled “Implant with Anatomically Conformed Trailing End,” thedisclosure of which is hereby incorporated by reference. Housing 401 hasinternal openings 446 proximate leading end 402 configured to supportrotatable members 420 and are preferably configured to have a widerdiameter portion 452 and a reduced diameter portion 454. Wider diameterportion 452 is configured to receive and support leading end 422 of arotatable member 420 while reduced diameter portion 454 acts as a stopto prevent rotatable member 420 from moving toward leading end 402 ofhousing 401.

Rotatable members 420 are positioned to either side of themid-longitudinal axis of housing 401. The rotatable members may beadapted to rotate in the same or opposite directions.

In FIGS. 13-15, another preferred embodiment of the implant of thepresent invention is shown and generally referred to by the referencenumber 500. Implant 500 has an external housing 501 with a leading end502 for insertion first into the disc space between two adjacentvertebral bodies of the human spine, a trailing end 504 opposite leadingend 502, an upper surface 506, a lower surface 508, and sides 510, 512between upper and lower surfaces 506, 508. Housing 501 of implant 500has a hollow interior 514 configured to hold bone growth promotingmaterial. In this embodiment, upper and lower surfaces 506, 508 eachpreferably have at least an arcuate portion 507 and at least anon-arcuate portion 509 near sides 510, 512. Non-arcuate portions 509 ofupper and lower surfaces 506, 508 are adapted to be oriented toward theendplates adjacent the disc space and are configured to support theadjacent vertebral bodies when implant 500 in inserted into the discspace. Arcuate portions 507 of upper and lower surfaces 506, 508 areadapted to be inserted into an implantation space formed across theheight of the disc space and into the adjacent vertebral bodies. Such animplantation space may be formed with a bone removal device, such as butnot limited to, a drill, a trephine, a reamer, a burr, and any otherbone removal device known to those skilled in the art suitable for itsintended purpose.

Upper and lower surfaces 506, 508, of implant 500 preferably each haveat least one opening 516 in communication with hollow interior 514 ofhousing 501 and adapted to permit the growth of bone from adjacentvertebral body to adjacent vertebral body through implant 500. Upper andlower surfaces 506, 508 further preferably have a plurality of openings518 configured to permit the passage therethrough of bone engagingprojections 532 described below from hollow interior 514 to the exteriorof housing 501. Sides 510, 512 of implant 500 can also have openings516.

Implant 500 has an internal rotatable member 520 configured to beinserted into hollow interior 514 of housing 501 preferably through anopening at trailing end 504 of implant housing 501. Alternatively,housing 501 of implant 500 need not be one piece, such as for examplehousing 501 may be split into upper and lower portions. With the upperand lower portions apart, rotatable member 520 can be placed into hollowinterior 514 and then housing 501 can be reassembled by putting togetherupper and lower portions and implant 500 can then be inserted into thedisc space. In this manner, bone engaging projections 532 may be atleast in part within the thickness of the wall of housing 501 when inopenings 518 and not extend beyond the exterior of implant 500 in theretracted position.

Rotatable member 520 is preferably substantially hollow and has aleading end 522, a trailing end 524, an exterior surface 526, and anopen interior 528. Trailing end 524 preferably is configured tocooperatively engage an instrument for rotating rotatable member 520such as, for example, an inserter similar to inserter 200 describedabove. Exterior surface 526 of rotatable member 520 preferably has atleast one opening 530 that permits bone to grow therethrough.Preferably, at least one of openings 530 in rotatable member 520 isconfigured to generally align with at least one of openings 516 inhousing 501 to allow bone to grow from adjacent vertebral body toadjacent vertebral body through housing 501 and through rotatable member520.

The upper and lower surfaces of rotatable member 520 have at least onebone engaging projection 532 adapted to penetrably engage the bone ofthe adjacent vertebral bodies similar to bone engaging projections 132described above. Bone engaging projections 532 are preferably configuredsuch that when rotatable member 520 is in a retracted position, implant500 may be linearly inserted into the disc space. After implant 500 isinserted into the disc space, rotatable member 520 is moved to adeployed position so that bone engaging projections 532 penetrablyengage into the adjacent vertebral bodies. The rotation of rotatablemember 520 can be limited to approximately 180 degrees or less about itsaxis of rotation so that it takes a half turn or less of the rotatablemember to deploy the bone engaging projections. By way of example onlyand not limitation, the rotation of rotatable member 520 can be limitedto a range of approximately 45 degrees to approximately 100 degrees tomove bone engaging projections from a retracted to a deployed position.

Bone engaging projections 532 are preferably oriented on opposite sidesof rotational member 520 and may, but need not, be diametricallyopposite one another. Bone engaging projections 532 may be arranged suchthat at least the apexes of two opposite bone engaging projections 532are on opposite sides of a mid-line passing therethrough. Such anover-center arrangement of bone engaging projections 532 creates a morestable configuration of the implant when the bone engaging projectionsare fully deployed. Greater energy is required to de-rotate a rotatablemember with opposed bone engaging projections when in an over-centerarrangement as the apex of each bone engaging projection has to be movedthrough the mid-line to move from a deployed to a retracted position.

As shown in FIG. 14A, interior surface 534 of hollow interior 514 ofhousing 501 preferably forms a pair of opposed abutment surfaces 536.Abutment surfaces 536 are configured to support and permit rotatablemember 520 to rotate within hollow interior 514 from a retracted to adeployed position to deploy bone engaging projections 532. The rotationof rotatable member 520 is limited when bone engaging projections 532contact abutment surfaces 536. The rotation of rotatable member 520 canbe limited to approximately 180 degrees or less about its axis ofrotation so that it takes a half turn or less of the rotatable member todeploy the bone engaging projections. Abutment surfaces 536 also may beconfigured to limit the rotation of rotatable member 520 toapproximately 90 degrees or less about its axis of rotation so that ittakes a quarter turn or less of the rotatable member to deploy the boneengaging projections. Interior surface 534 of hollow interior 514preferably has spaces configured to receive bone engaging projections532 in the retracted position such that the apex of each bone engagingprojection is substantially in a corner of hollow interior 514. In thisposition, the bone engaging projections are retained substantiallywithin the hollow interior of housing 501.

In FIG. 14B, another preferred embodiment of the implant in accordancewith the present invention is shown and generally referred to by thereference number 500′. Implant 500′ is similar to implant 500, exceptthat upper and lower surfaces 506′, 508′ each preferably having at leasttwo arcuate portions 507′ and at least some non-arcuate portion 509′either between or lateral to arcuate portions 507′ and/or near sides510′, 512′. Non-arcuate portions 509′ of upper and lower surfaces 506′,508′ are adapted to be oriented toward the vertebral bodies and, ifstill present, the endplates adjacent the disc space and are configuredto support the adjacent vertebral bodies when implant 500′ is insertedinto the disc space. Arcuate portions 507′ of upper and lower surfaces506′, 508′ are preferably located on opposite sides of themid-longitudinal axis of implant 500′. Such a configuration helps tofurther reduce or eliminate any potential rocking motion that mightotherwise occur with an implant having a centrally placed single arcuateportion. Arcuate portions 507′ may be generally parallel to each otheror at an angle to each other. Having two or more arcuate portions 507′provides for more surface area of implant 500′ to contact the bone ofthe adjacent vertebral bodies and may also provide for access to thevascular bone of the adjacent vertebral bodies. Implant 500′ having atleast two arcuate portions 507′ has a height that is less than animplant with a single arcuate portion having the same combined width oftwo arcuate portions 507′. Furthermore, implant 500′ having at least twoarcuate portions 507′ provides the added advantage of utilizing thestronger more dense bone of the adjacent vertebral bodies located closerto the disc space.

Implant 500′ preferably has at least two internal rotatable members 520′configured to be inserted into hollow interior 514′ of housing 501′preferably through an opening at one of the trailing and leading ends ofimplant housing 501′ or the implant may be opened, such as by way ofexample only by having the upper and lower portions of the housingconfigured to be separable, to permit the placement of rotatable members520′ into hollow interior 514′. Then, housing 501′ can be reassembled byputting together upper and lower portions and implant 500′ can then beinserted into the disc space.

In FIGS. 16-19, another preferred embodiment of the implant of thepresent invention is shown and generally referred to by the referencenumber 600. Implant 600 is similar to implant 500 except for theconfiguration of bone engaging projections 632. Bone engagingprojections 632 preferably have a base portion that extends fromrotatable member 620 and terminates in a larger dimension upper portion.The upper portion of bone engaging projection 632 preferably has atransverse cross sectional dimension that is greater than the transversecross sectional dimension of the base portion. By way of example onlyand not limitation, the base portion and the upper portion of boneengaging projection 632 can have a T-shaped cross section as shown inFIG. 19. The transverse cross sectional configuration of bone engagingprojections 632 can have other configurations, including but not limitedto, C-shaped, V-shaped, W-shaped, Y-shaped, and any other configurationsuitable for the intended purpose. Bone engaging projections 632preferably have a leading edge 633 that is at least in part curved andthe upper portion of bone engaging projection 632 is preferably taperedproximate leading edge 633 to facilitate penetration of bone engagingprojection 632 into the bone of the vertebral bodies. Similarly,openings 618 preferably have a configuration shaped to permit boneengaging projections 632 to extend from hollow interior 614 of housing601 and through openings 618 when deployed.

Implant 600 is inserted into the disc space and bone engagingprojections 632 are deployed to penetrably engage the bone of theadjacent vertebral bodies. The configuration of bone engagingprojections 632 provide for increased stability of the implant relativeto the adjacent vertebral bodies and of the vertebral bodies relative toeach other. Further, the configuration of bone engaging projections 632limit the ability of the vertebral bodies to move apart from one anotherto further enhance stability.

As shown in FIG. 20, in a further variation, the upper portion of theT-shaped configuration of bone engaging projections 632′ increases inthickness at least in part from leading edge 633′ to trailing edge 635′so that it is closer to the housing of implant 600 in the deployedposition and brings the vertebral bodies closer together so as tocompressively load the vertebral bodies towards the implant when thebone engaging projections are fully deployed. In this configuration theupper portion of bone engaging projection 632′ has a decreased distancefrom housing of the implant at its trailing edge than at its leadingedge when the bone engaging projections are in the deployed position.

As shown in FIG. 21, in a further alternative configuration, boneengaging projections 632″ have a lower portion opposite the upperportion of the T-shaped configuration. The lower portion of the T-shapedconfiguration has an arc of radius that is less than the arc of radiusof the upper portion of the T-shaped configuration resulting in adecreased distance from the housing of the implant proximate trailingedge 635″ than proximate leading edge 633″ when bone engagingprojections 632″ are in the deployed position. Such a configuration ofbone engaging projections 632″ provides for the compressive loading ofthe vertebral bodies towards the implant when the bone engagingprojections are fully deployed.

In FIGS. 22 and 23, another preferred embodiment of the implant of thepresent invention is shown and generally referred to by the referencenumber 700. Implant 700 is similar to implant 600 except for theconfiguration of housing 701. Each of upper and lower surfaces 706, 708of housing 701 preferably has an open area in communication with hollowinterior 714 of housing 701. The open area preferably forms a window 703(a large opening) in each of upper and lower surfaces 706, 708 over atleast a portion of rotatable member 720. Rotatable member 720 is exposedto the adjacent vertebral bodies through windows 703. Rotatable member720 may project at least in part through the windows 703 to contact theadjacent vertebral bodies. In a preferred embodiment, rotatable member720 may protrude at least in part through windows 703 to be flush withthe exterior of housing 701. Housing 701 is preferably configured to beopened to receive rotatable member 720 therein and closed to holdrotatable member 720 at least in part within housing 701. By way ofexample only and not limitation, housing 701 may be separable into upperand lower portions at seam 705.

In FIGS. 24 and 25, another preferred embodiment of the implant of thepresent invention is shown and generally referred to by the referencenumber 800. Implant 800 is similar to implant 100 except that itpreferably has at least two internal rotatable members 820 for deployingbone engaging projections 832 through upper and lower surfaces 806, 808of housing 801. Rotatable members 820 are preferably at least in partwithin hollow interior 814 of housing 801 proximate upper and lowersurfaces 806, 808, respectively. Rotatable members 820 are preferablyheld in rotational relationship to housing 801 by support structures809. Each of rotatable members 820 preferably have at least one end 824configured to cooperatively engage an instrument for rotating rotationalmembers 820 to deploy bone engaging projections 832. The rotation ofrotatable member 820 can be in the preferred range of approximately 200degrees to approximately 25 degrees about its axis of rotation so thatit takes less than a full turn of the rotatable member to deploy thebone engaging projections. By way of example only and not limitation,rotational member 820 can be rotated more than 180 degrees, for exampleapproximately 195 degrees, to deploy bone engaging projections 832 in anover center position. While rotational members 820 can be solid or atleast in part hollow, in this instance a generally solid configurationis preferred so that each of rotational members 820 preferably has arelatively small cross sectional dimension transverse to itslongitudinal axis such that rotational members 820 occupy only a smallportion of the interior of housing 801.

Housing 801 of implant 800 preferably has at least a portion along itslongitudinal axis that has a generally square cross section transverseto the longitudinal axis. It is appreciated that housing 801 can have agenerally rectangular cross section or other cross-sectionalconfiguration suitable for its intended purpose. The implant may beinserted into the disc space on its side and then flipped 90 degrees toorient the upper and lower surfaces of the implant toward the adjacentvertebral bodies, respectively. Such an implant would preferably have areduced dimension between a pair of diagonally opposed corners. Forexample, such an implant could have diagonal corners that are rounded tofacilitate the 90 degree rotation of the implant between the adjacentvertebral bodies as taught by Michelson in U.S. application Ser. No.09/429,628 for a “Self-Broaching, Rotatable, Push-In Interbody SpinalFusion Implant and Method for Deployment Thereof”, the portions of thespecification directed to the reduced dimension between a pairdiagonally opposed corners are hereby incorporated by reference herein.Upper and lower surfaces 806, 808 of implant 800 are preferably at leastin part non-arcuate and are generally parallel to each other along atleast a portion of the longitudinal axis of implant 800. Alternatively,upper and lower surfaces 806, 808 can be angled relative to one anotheralong at least a portion of the longitudinal axis of implant 800.

FIGS. 1-5 show various steps of a preferred method for inserting implant100 from a posterior approach to the spine and using associatedinstrumentation disclosed herein.

By way of example and not limitation, preferred steps of methods forinstalling the implants of the present invention include but are notlimited to the steps summarized below.

1. Identifying the disc space to be operated upon;2. Providing access to the disc space;3. Utilizing a guard or retractor to provide protected access to thedisc space;4. Removing sufficient disc material to allow an implant to be insertedat least in part within and across the height of the disc space;5. Distracting the disc space between the vertebral bodies to generallyrestore the height of the disc space with or without the use of adistractor;6. Utilizing a guard with disc penetrating extensions to provideprotected access to the disc and to distract the vertebral bodiesadjacent the disc space;7. Working upon the endplates of the adjacent vertebral bodies, whichmay include for example scraping the endplates, decorticating theendplates, or cutting away at least a portion of the endplates;8. Attaching the implant to an implant inserter;9. Inserting the implant at least in part into the disc space;10. Loading the implant with bone growth promoting material: (i) priorto implantation of the implant, (ii) after implantation of the implant,or (iii) both prior to implantation and after implantation of theimplant;11. Packing bone growth promoting material around the implant andpushing bone through the implant and into the area around the implant;12. Rotating the hollow internal member to deploy the bone engagingprojections to penetrably engage the vertebral bodies adjacent the discspace, which may include rotating the internal member less than 180degrees;13. Removing the inserter from the implant; and/or14. Repeating the procedure at same disc level if necessary.

The methods for installing the implants of the present invention are notlimited to the steps identified above, need not include all the stepsrecited above, and need not be performed in the order listed above. Byway of example only and not limitation, two implants may be insertedinto the disc space before either has its internal rotatable memberrotated to deploy the bone engaging projections, or the implant may beinserted into the disc space prior to being packed with bone growthpromoting material or prior to the bone growth promoting material beingforced through the openings in the implant. Other methods for installingimplants known to those skilled in the art may be used to install theimplants of the present invention may be used without departing from thescope of the present invention.

Preferred instruments and methods of preparing the disc space aredisclosed and taught by Michelson in U.S. Pat. No. 6,159,214 entitled“Milling Instrumentation and Method for Preparing a Space BetweenAdjacent Vertebral Bodies”; U.S. Patent Application No. 60/255,463entitled “Spinal Interspace Shaper”; U.S. Pat. No. 6,083,228 entitled“Device and Method for Preparing a Space Between Adjacent Vertebrae toReceive an Insert”; U.S. Pat. No. 6,224,607 entitled “Instrument andMethod for Creating an Intervertebral Space for Receiving an Implant”;and WIPO publication WO 99/63891 entitled “Device for Preparing a SpaceBetween Adjacent Vertebrae to Receive an Insert,” the disclosures ofwhich are all herein incorporated by reference. It is appreciated thatother instruments and methods may be used to prepare the disc space toreceive the implant of the present invention.

Where it is desirable, the surgeon may utilize a guard such as guard 500shown in FIG. 1 for protecting adjacent delicate neurologicalstructures. Guard 500 may be left in place after the preparation of thedisc space such that the described operation can be performed throughguard 500 and be removed at its completion. The implantation space mayhave any configuration suitable to receive the implant to be insertedtherein.

Prior to preparing the disc space, if it is desirable, the surgeon maydistract the vertebral bodies with a distractor having disc penetratingextensions such as that taught by Michelson in U.S. Pat. No. 5,484,437entitled “Apparatus and Method of Inserting Spinal Implants” and U.S.Pat. No. 5,797,909 (the '909 patent), entitled “Apparatus for InsertingSpinal Implants,” the disclosures of which is herein incorporatedreference. If necessary, the surgeon may impart an angulation to theadjacent vertebral bodies with a distractor having disc penetratingextensions with angled upper and lower surfaces such as that taught inthe '909 patent to Michelson.

As shown in FIGS. 2 and 5, rotatable member 120 may be inserted intohollow interior 114 of implant 100 and distal end 204 of inserter 200 iscooperatively engaged to trailing end 104 of implant 100 such that tabs214 of implant engagement surface 212 are engaged with grooves 140 ofimplant 100. It is appreciated that rotatable member 120 may be insertedinto hollow interior 114 of housing 101 after implant 100 is insertedinto the disc space. Implant 100 is inserted into the disc spacepreferably by linear insertion without substantial rotation of implant100 to the appropriate depth as desired by the surgeon. Alternatively,the implant be can be rotated at least in part during its implantationinto the disc space, but is not screwed into the disc space. Forexample, the implant may be inserted into the disc space on its side andthen rotated 90 degrees to place the upper and lower surfaces of housing101 in contact with the adjacent vertebral bodies, respectively. Boneengaging projections 132 can then be deployed. Trailing end 104 ofimplant 100 preferably does not protrude beyond the posterior aspects ofthe adjacent vertebral bodies, and preferably no substantial portion ofimplant 100 protrudes from the outer perimeter of the adjacent vertebralbodies. During insertion of implant 100, bone engaging projections 132are retained in the retracted position to facilitate linear insertion ofimplant 100 into the disc space.

After implant 100 is properly positioned in the implantation space, thebone engaging projections 132 can be deployed. In a preferredembodiment, inner shaft 224 of inserter 200 is rotated by the surgeon torotate rotatable member 120 of implant 100 from a retracted position toa deployed position so that bone engaging projections 132 extend throughupper and lower surfaces 106, 108 of implant 100 to penetrably engagethe end plates of the adjacent vertebral bodies and prevent theexpulsion of the implant from the disc space. In a preferred embodiment,rotatable member 120 is rotated one half turn or less to deploy the boneengaging projections.

Implant inserter 200 is detached from implant 100 and removed. A cap maybe installed to close at least part of the implant's trailing end toprevent bone from growing into the spinal canal, or to limit adhesionsof the neurological structures at the canal floor, or to otherwiseprotect the neurological structures. One of the purposes for a capincludes restricting the passage of fusion-promoting materials so thatthey remain loaded within the implant.

Preferably prior to insertion, hollow interior 114 of implant 100 andopen interior 128 of rotatable member 120 may be loaded with fusionpromoting materials including any of, or any combination of, bone in anyof its forms, materials derived from bone, bone morphogenetic proteins,mineralizing proteins, genetic materials coding for the production ofbone or any substance capable of inducing the formation of bone oruseful for achieving fusion for the intended purpose. The fusionpromoting materials may be loaded or preferably compressively loadedinto hollow interior 114 of implant 100 and/or open interior 128 ofrotatable member 120 by use of an instrument such as, for example, atamp, press, or piston at any time during the procedure as desired bythe surgeon. Additionally, scar tissue-inhibiting and/or antimicrobialmaterials may be applied to the implant.

When said methods and instrumentation are used to install such implantsposteriorly, the technique may further include the application of scartissue inhibiting substances posterior to the implant trailing end andat the floor of the spinal canal.

When performing the procedure from a posterior approach to the spine, itis generally preferred that the procedure be performed on both sides ofthe saggital midline of the disc space and that two implants 100, eachhaving a width less than half the width of the disc space be insertedfrom a posterior to anterior approach either generally parallel oralternatively from a generally posterior to anterior approach in a“toed-in” configuration. Having completed the procedure on a first side,the procedure is then repeated as already described on the opposite sideof the saggital midline of the same disc space leading to theimplantation of two implants 100 in the same disc space.

If implants 300 are being inserted into the disc space, then theprocedure may preferably include distracting the adjacent vertebralbodies to impart an angulation to the adjacent vertebral bodies with adistractor such as that taught in the '909 patent to Michelson toaccommodate the insertion of each of implants 300. In anotheralternative method, both implants may be implanted from an anteriorapproach to the spine using many of the same steps already described.

When performing the method from the anterior approach, a plurality ofimplants 100 or 300 (for example two or three) or a single implant suchas implant 400 may be used as the spinal cord is not in the path ofinsertion of the implant. When using a laparoscope or when it isdifficult to mobilize the great vessels two or more smaller implants maybe used in order to use a smaller working space.

The various features of the preferred embodiments of the presentinventions described herein are combinable with one another and are notlimited to a particular embodiment of the implant for which the featuresare described. By way of example only and not limitation, it isappreciated that for any of the embodiments of the implants of thepresent invention, the external housing may be formed of two or morepieces that can be separated to permit insertion of the internalrotatable member within the housing and then reassembled forinstallation into the disc space; and the various embodiments of thebone engaging projections described herein may be utilized with any ofthe embodiments of the implants of the present invention.

The spinal fusion implant of the present invention may comprise of anyartificial or naturally occurring implant material suitable forimplantation in a human being. The implant of the present invention canbe formed of a material such as metal including, but not limited to,titanium and its alloys, surgical grade plastics, composites, ceramics,or other materials suitable for use as a spinal fusion implant. Theimplant of the present invention can comprise at least in part of amaterial that is resorbable by the human body. The implant of thepresent invention can be formed at least in part of a porous material orcan be formed at least in part of a material that intrinsicallyparticipates in the growth of bone from one of adjacent vertebral bodiesto the other of adjacent vertebral bodies.

Further, the implant of the present invention may be comprised of,treated with, coated, or filled with a fusion promoting substance. Theimplant may be used in combination with a fusion promoting substanceincluding, but not limited to, bone, bone derived products,demineralized bone matrix, ossifying proteins, bone morphogeneticproteins, hydroxyapatite, and genes coding for the production of bone.

Where such implants are for posterior implantation, the trailing ends ofsuch implants may be treated with, coated with, or used in combinationwith substances to inhibit scar tissue formation in the spinal canal.The implants of the present invention may be adapted to facilitate theelectrostimulation of the implant or a portion thereof and/or of thefusion area into which they are inserted and the proximate bonethereabout. The implant of the present invention may be comprised atleast in part of, coated with, or used in combination with materials tomake it antimicrobial, such as, but not limited to, antibiotics, silverions or any other substance suitable for the intended purpose.

There is disclosed in the above description and the drawings implantsand instruments and methods for use therewith, which fully andeffectively accomplish the objectives of this invention. However, itwill be apparent that variations and modifications of the disclosedembodiments may be made without departing from the principles of theinvention.

What is claimed is:
 1. An interbody spinal implant comprising: a bodyhaving an upper portion and a lower portion, said upper portion having afirst arcuate portion, a second arcuate portion, and a non-arcuateportion separating said first and second arcuate portions, each of saidarcuate portions including a plurality of recesses; and first and secondrotatable shafts positioned at least in part within said first andsecond arcuate portions, respectively, each of said first and secondrotatable shafts having an axis of rotation, each of said rotatableshafts including a plurality of spaced-apart bone engaging projections,said first and second rotatable shafts each being rotatable from anundeployed position wherein said bone engaging projections arepositioned at least in part within said body of the implant to adeployed position wherein said bone engaging projections are positionedat least in part outside of said body of the implant, said bone engagingprojections extending through respective ones of said recesses and intobone when in the deployed position.
 2. The spinal implant of claim 1,wherein the axes of said first and second rotatable shafts are parallelto one another in a single horizontal plane.
 3. The spinal implant ofclaim 1, wherein said body has a height from said lower portion to saidupper portion, and a width transverse to the height, the width of saidbody being greater than the height of said body.
 4. The spinal implantof claim 1, wherein said lower portion of said body is symmetrical tosaid upper portion of said body relative to a horizontal plane bisectingsaid implant.
 5. The spinal implant of claim 1, wherein each of saidrotatable shafts has a maximum diameter greater than a minimum height ofsaid implant.
 6. The spinal implant of claim 1, wherein each of saidrotatable shafts has a length, said plurality of bone engagingprojections being spaced along a majority of the length of eachrotatable shaft.
 7. The spinal implant of claim 1, wherein said boneengaging projections have a uniform shape.
 8. The spinal implant ofclaim 1, wherein said implant is a spinal fusion implant.
 9. The spinalimplant of claim 1, wherein said implant includes a hollow interior,said recesses being in communication with said hollow interior.
 10. Thespinal implant of claim 1, in combination with hydroxyapatite.